Rectifying detector for high-frequency alternating electric currents



1.. E. THOMPSON ET AL 59 RECTIFYING DETECTOR FOR HIGH-FREQUENCY ALTERNATING ELECTRIC CURRENTS I Filed Aug. 18f 1945 INVENTORS [wile 17294"! Ylzampma am? BY Alemnaepfizzfims' 7 /1/5 13 ATTORN EY Patented Dec. 16, 1947 UNITED STATES PATENT OFFICE RECTIFYING DETECTOR FOR HIGH-FRE- QUENCY ALTERNATING ELECTRIG CUR RENTS Vania Application August 18, 1943, Serial No. 499,120 In Great Britain August 26, 1942 19 Claims.

This invention relates to rectifying detectors for high frequency alternating electric currents and more particularly to detectors of the point contact or so-called crystal type for radio frequency currents, the invention having for its object to provide an improved form of detector de vice of this character.

Galena or lead sulphide in the form of a natu ral or artificially prepared crystal was employed as a radio detector many years ago and the invention utilises this compound prepared in a special manner preferably with the addition of other substances for a detector device giving important advantages and enabling the rectifying action to be effectively controlled.

According to the principal feature of the invention a rectifying or detector element is formed by precipitating the lead sulphide in a crystalline condition which is subsequently ground and the resulting powder compressed and utilised as a detector crystal in conjunction with a catswhisker or counter-electrode preferably of steel.

According to a further feature of the invention a relatively small amount of chlorine is added to the lead sulphide preferably by the addition of a suitable chloride prior to the precipitation process. Other substances may also be added during the manufacture of the detector element.

According to a still further feature of the invention the lead sulphide with or without the addition of other substances and after precipitation into a crystalline condition is heated to a temperature of between 400 C. and 1000 C. and, after being ground and compressed, is subjected to a second heat treatment during which a tem- :1.

line sodium sulphide per litre of distilled water.

c. c. of solution (a) is added to 50 c. c. of neutral water (pH 8) and to this is added 10 c. c. of solution (b) at room temperature.

The resultant black precipitate and solution are heated to boiling point and filtered hot through 2 coarse filter paper. The precipitate is then washed with 150 c. c. of boiling distilled water and placed in a clean dry crucible into which is poured 1 c. c. of solution (11) and the whole mixed into a uniform paste.

The crucible and its contents is then heated to 600-700" C. for 12 minutes in an air oven and the crucible allowed to cool with the lid on.

After cooling the black residue is removed from the crucible, ground to a fine powder and intimately mixed with '7 grms. of flowers of sulphur (the amount of sulphur employed may exceed the amount of the lead sulphide).

A crucible is placed in an air oven maintained at a temperature of 900-1000 C. and is raised to the oven temperature. The mixture of sulphide and sulphur is placed in the crucible and the sulphur is burnt oii at the exit of the oven.

Immediately the sulphur has been driven off which takes place in approximately one minute, the crucible is removed from the oven and the powder is removed from the crucible being now ready for the pressing operation, which consists in placing the powdered material into a die or mould constructed of steel or brass and compressing the material by a series of impacts by a weighted plunger. For producing a pellet of inch diameter approximately 100 taps with a weight of 1.5 kg. falling through one inch is found to give satisfactory results.

The compressed pellet thus formed is then heated toa dull red heat in a Bunsen flame and after cooling the surface of the pellet is burnished with thallium metal. The pellet is then re-heated to a red heat and the top surface is removed with a file. The new surface is burnished on paper and annealed two or three times in a Bunsen flame for 15 seconds, care being taken that the temperature of the pellet is not allowed to exceed a red heat.

In order to control the characteristics of the detector by the addition of a small amount of chlorine a suitable chloride may be added to the lead acetate solution prior to the precipitation r of the lead sulphide, the amount of chlorine added being up to from 0.005% to 0.1%. Particularly favourable results are obtained by the addition of 0.04% chlorine. An excess of sulphur in the solution during precipitation is also found to be advantageous and an excess of sodium sulphide (approximately may be employed for this purpose.

The addition of a small quantity of iron (normally present in commercial flowers of sulphur) to the lead sulphide is found to be of advantage 3 the most favourable quantity being of the order of 0.5% but may be from 0.3% to 4.0%, the iron being added by evaporating a solution of an iron salt in contact with the lead sulphide, during the drying of the sulphide.

The iron may also be added to the lead sulphide during the grinding process above de-, scribed.

The addition of thallium to the sulphide may be effected either by the burnishing process above described or by adding a solution of a suitable thallium salt to the solution (a) above referred to, so that when solutions (a) and (b) are mixed together, the resultant precipitate is a mixture of lead sulphide and thallium sulphide.

Advantageous results are obtained by this addition of thallium to the amount of from 0.3% to 4.0%.

The thallium in the form of a thallium salt may also be added mechanically to the precipitate of lead sulphide by an evaporation process as in the case of iron. Alternatively the thallium may be added in the form of a suitable salt to the lead sulphide during the grinding operation above described or a film of thallium or a thallium salt may be deposited on the surface of thecompressed lead sulphide prior to the second heat treatment.

In utilising the pellet produced as above de scribed, the pellet i (see drawing) is preferably mounted in a metal bushing 2 which is screwed into an outer casing 3 to the top of which the upper end of the cats whisker contact electrode 4 is secured, this electrode comprising a helical spring carrying at its lower end the point steel contact element la resting on the upper surface of the pellet. The casing above the pellet is preferably filled with mineral fat or jelly ,5 which facilitates assembly and stabilises the electrode in operative position.

The detector pel et thus obtained is utilised for rectification in conjunction with a counter-electrode consisting of a sharp steel point resting on the burnished and treated surface of the pellet with a pressure of 100-300 grins, the point being as sharp as possible.

Instead of forming the lead sulphide composi tion prepared as above described into a pellet, the material may be pressed onto a roughened metal base or support. Alternatively, the material may be pressed as a pellet and an electrode prepared on it by rendering a ortion of the surface of the pellet non-rectifying by removing the surface layer and depositing thereon a conducting electrode by cathodic sputtering, metal spraying, electro-plating or the application of colloidal graphite,

The invention is evidently not limited to the particular processes above described by way of example which may be varied as desired to meet particular conditions Without exceeding the scope of the invention.

Having thus described our invention, what we claim as new and desire to secure by Letters Patcut is:

1. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, wh ch process consists in precipitating in a crystalline condition lead sulfide, subsequently grinding it and then compressing the resulting powder.

2. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide, heating the lead sulphide. to a temperature 4 lying between 400 C. and 1000 C., grinding the lead sulphide into a powder, and then compressing the powder and subjecting it to a, second heat treatment during which a temperature lying be- I tween 400 C. and 1120 C. is reached.

3. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide to which chlorine has been added, grinding the precipitated lead sulphide, and then compressing the resulting powder.

4. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide to which between 0.005% and 0.1% of chlorine has been added, subsequently grinding the precipitated lead sulphide, and then compressing the resulting powder.

5. The process for preparing a rectifying detector of the crystal type for h gh frequency alternating electric currents, which process consists in precipitatin in a crystalline condition lead sulphide to which chlorine in the form of a suitable chloride has been added, subsequently grinding the precipitated lead sulphide, and then compressing the resulting powder.

6. The process for preparing a rectifying detector of the crystal type for high frequency alternating electr c currents, which process consists in precipitating in a crystalline condition lead sulphide to which between 0.005% and 0.1% of chlorine in the form of a suitable chloride has been added subsequently grinding the precipitated lead sulphide and then compressing the resulting powder.

7. The process for preparing a rectifying detector of the crystal type for h gh frequency alternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide to which thallium has been added, subsequently grinding the precipitated lead sulphide, nd then compressing the resulting powder.

8. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide to which from 0.3% to 4.0% of thallium has been added, subsequently grinding the precipitated lead sulphide, and then compressing the resulting powder.

9. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide to which thallium in the form of a suitable salt has been added. subsequently grinding the precipitated lead sulphide, and then grinding the resulting powder.

10. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide, grinding the precipitated lead sulphide, adding thallium during the grinding operation, and then compressing the resulting powder.

11. The process for preparing a rectifying detector for high frequency alternating electric currents of the crystal type, which process consists in precipitating in a crystalline condition lead sulphide, heatin the precipitated lead sulphide to a temperature lying between 400 C. and 1000 C., grinding it into a powder, compressing the powder, depositing a film of thallium or thallium salt on the surface of the compressed lead sulphide, and then subjecting the resulting product to a second heat treatment during which a temperature between 400 C. and 1120 C. is reached.

12. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide to which iron has been added, subsequently grinding the precipitated lead sulphide, and then compressing the resulting powder.

13. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide to which between 0.3% and 4.0% of iron has been added, grinding the precipitated lead sulphide, and then compressing the resulting powder.

14.. The process for preparing a rectifying detector of the crystal type for high frequency a1- ternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide to which iron in the form of a suitable salt has been added, subsequently grinding the precipitated lead sulphide, and then compressing the resulting powder.

15. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide, grinding the precipitated lead sulphide, adding iron in the form of a suitable salt during the grinding operation, and then compressing the resulting powder.

16. The process for preparing a rectifying detector of the crystal type for high frequency alter- .nating electric currents, which process consists in precipitating in a crystalline condition lead sulphide, grinding the precipitated lead sulphide, and then compressing the resulting powder onto a metal base or support.

17. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, which process consists in precipitating in a crystalline condition lead sulphide, subsequently grinding the precipitated lead sulphide, and then compressing the resulting powder into a pellet supported on a roughened metal base.

18. The process for preparing a rectifying detector of the crystal type for high frequency alternating electric currents, which process consists in precipitating in a crystalline lead sulphide, subsequently grinding the precipitated lead sulp id compressing the resulting powder into a pellet, and preparing a non-rectifying area on said pellet by removing the surface layer from said area and depositing a conducting electrode.

19. The process for preparing a rectifying detector for high frequency alternating electric currents of the crystal type, which process consists in precipitating in a crystalline condition lead sulphide, heating the lead sulphide to a temperature lying between 400 C. and 1000 C., grinding it into a powder, compressing the powder into a pellet and subjecting it to a second heat treatment during which a temperature lying between 400 C. and 1120 C. is reached, said pellet having a non-rectifying area prepared on it by removing the surface layer from said area and depositing a conducting electrode.

LESLIE E. THOMPSON. ALEXANDER JENKINS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

